Method of cleaning nonferrous alloys



Fatented I Dec. 18,1934

UNITED STATES METHOD OF CLEANING NONFERRDUS ALLOYS Leonard 0. Larsen,Downers Grove, 11]., assignor to Western Electric Company, Incorporated,

New York, N. Y., a corporation of New York No Drawing. ApplicationDecember 30, I932,

Serial No. 649,596

Claims.

This invention relates to a method of cleaning non-ferrous alloys, suchas brass, bronze and similar alloys.

In the process of cleaning non-ferrous alloys by the acid dip method, itis customary to use sulfuric acid, nitric acid or a mixture of sulfuricand nitric acids. When parts dipped in such a bath are exposed to theatmosphere during the clipping process, they often become discolored orstained.

An object ofthe invention is to provide an expedient and eficient methodof cleaning nonferrous alloy parts.

In accordance with one embodiment of the invention, brass or phosphorbronze parts are dipped in a bath comprising a mixture of sulfuric,nitric and phosphoric acid and upon removal from the bath the parts arerinsed in water, subjected to asodium cyanide bath to neutralize anyremaining acid, and again rinsed in water and dried. This process leavesthe parts bright and without stains.

A complete understanding of the invention will be obtained from thefollowing detailed description.

When brass and phosphor bronze parts are acid dipped .manually, theparts are usually placed in a basket and immersed in a bath of sulfuricacid or a mixture .of sulfuric acid and nitric acid. The parts are thenagitated inthe basket while they are immersed. During withdrawal of thebasket from the bath agitation of the parts is avoided as much aspossible so that they will be surrounded by acid fumes while exposed tothe atmosphere in transferring the parts to a rinsing bath of water. Inautomatic machine dipping, the parts are in some instances agitated inthe acid bath by dropping or pouring them into a basket immersed in theacid bath, and in this manner the entire agitation of the parts isprovided for. When the basket is withdrawn from the acid bath, the partsare transferred to another basket immersed in a rinsing water bath bypouring the parts from the first basket into the second basket andconsequently the parts are agitated while in the air whereby the acidfumes surrounding the parts are dispersed and the parts are exposed tothe atmosphere causing discoloration and staining of the parts. Thisappears to be due to the fact that a dilute acid attacks the zinc in thebrass or the tin in the bronze to a greater extent than the copper inthese alloys, leaving copper stains on the surface of the parts. As longas the parts are in the bath, the spent (Cl. ES -8) acid in contact withthe surface of the parts is replenished by more concentrated acid in thebath. However, it is believed that when the parts are removed from thebath, only a small amount of the-acid adheres to the parts and thisquickly becomes diluted due to the formation of metallic sulphates andnitrates, and consequently stains are formed upon the parts.

It has been found that when an inhibiting agent, such as a phosphoruscompound, preferably phosphoric acid, is added to the acid bath, theparts maybe exposed to the air after dipping in the acid bath withoutthe appearance of stains or discoloration on the parts. This also makesthe present process particularly applicable to cleaning parts which areto be electroplated since the parts may be attached to theelectroplating racks and dipped into the cleaning bath. On account ofthe spacing of. the parts on the electroplating rack, they willnecessarily be exposed to the atmosphere on removal from the bath.However, the addition of the inhibiting agent prevents the formation ofstains on the parts when exposed to the air. While either sulfuric ornitric acid may be used, it is preferable to use a mixture of thesulfuric and nitric acids. These acids may be mixed in variousproportions, and phosphoric acid added in accordance with theconcentration of the bath. A suitable mixture has been found to consistof sulfuric acid, 36% nitric acid and 14% phosphoric acid.

The process is exothermic and the bath usually rises above roomtemperature. Ordinarily no temperature control of the bath is necessary.

As a specific example of carrying out the process of the invention,brass or bronze parts may be poured into a basket and immersed'in amixture of sulfuric, nitric and phosphoric acids. The basket is thenwithdrawn from the bath and the parts are poured into a basket immersedin a water rinsing bath. From the rinsing bath the parts are removed inthe basket and poured into a bath of sodium cyanide to neutralize anyacid 45 that has not been removed in the rinsing bath. The parts arethen removed from the cyanide. bathand again rinsed whereupon they maybe dried by a heated current of air.

, While the invention has been described in con- 50 nection with brassand bronze articles, it will be evident that it is equally applicable toother non-ferrous alloys containing copper, zinc or tin. Although theinvention is especially advantageous in connection with automaticdipping methods, it also has utility when manual dipping is employed.

What is claimed is:

1. A method of cleaning non-ferrous alloys containing copper and anotherconstituent selected from the elements zinc and tin which comprisessubjecting the alloy to the action of a bath containing sulfuric acidand phosphoric acid.

2. A method of cleaning a non-ferrous alloy containing zinc insubstantial amounts which comprises subjecting the alloy to the actionof a mixture of sulfuric acid, nitric acid, and phosphoric acid.

3. A method of cleaning a non-ferrous zinc alloy which comprisesimmersing the alloy in a bath containing sulfuric and phosphoric acid,removing the alloy therefrom and permitting it to drain while exposed tothe atmosphere, and transferring the alloy to a rinsing bath.

4. A method of cleaning non-ferrous alloys containing copper and otherconstituents selected from the elements zinc and tin which comprisessubjecting the alloy to the action of a bath containing nitric acid andphosphoric acid.

5. A method of cleaning or pickling alloy metal containing copper and ametal of the group of zinc or tin which comprises subjecting the same toan acid pickling or cleaning bath and inhibiting the chemical action ofthe acid on the metal by the addition of phosphoric acid withoutinterfering with the cleaning or pickling action of the bath and therebyreducing the formation of copper stains on the parts by incorporating inthe acid bath a substantial amount of an inhibiting acid.

LEONARD O. LARSEN.

